I think it's just a matter of things being TFLified. In that take crossrail for example. We can argue the lack of toilets, luggage racks, seating layout, no bins etc is fine for the length of journey but we all know if it wasn't operated through TFL the 345s would have all those things and be a copy of the 700s. A positive to things being TFLified is that they understand it's well and good to have standing space but you need to provide plenty of grab poles which they do on almost all of their stock.
I personally don't mind longitudinal seating, at least there's almost always armrests to segregate your space (at least in London, obviously not in NY etc). It may very well be that longitudinal seating is cheaper to provide but either way, it certainly does maximise the sense of space. Walking through a 345s longitudinal only carriages and it almost doesn't feel like a UK train, it feels too wide, and as spacious as the 700s are, you won't get that with transverse in my opinion.
I wouldn't mind doing the route from say southbury to Liverpool Street longitudinal IF the seats were padded which they simply aren't. On fainsa seating, you can feel a small amount of padding but still acknowledge there simply isn't enough for long journeys, at least you get a proper backrest, but on these TFL aventura seats, there simply is none it feels like. I'd happily sit from Ealing Broadway to upminster on the s stock because their seats are well padded. Still it's completely objective as some really like the 345s seats.